1. Field of Invention
The present invention relates generally to an improved method of and system for illuminating moving and well as stationary objects, such as parcels, during image formation and detection operations, and also to an improved method of and system for acquiring and analyzing information about the physical attributes of such objects using such improved methods of object illumination, and digital image analysis.
2. Brief Description of the State of Knowledge in the Art
The use of image-based bar code symbol readers and scanners is well known in the field of auto-identification. Examples of image-based bar code symbol reading/scanning systems include, for example, hand-hand scanners, point-of-sale (POS) scanners, and industrial-type conveyor scanning systems.
Presently, most commercial image-based bar code symbol readers are constructed using charge coupled device (CCD) image sensing/detecting technology. Unlike laser-based scanning technology, CCD imaging technology has particular illumination requirements which differ from application to application.
Most prior art CCD-based image scanners, employed in conveyor-type package identification systems, require high-pressure sodium, metal halide or halogen lamps and large, heavy and expensive parabolic or elliptical reflectors to produce sufficient light intensities to illuminate the large depth of field scanning fields supported by such industrial scanning systems. Even when the light from such lamps is collimated or focused using such reflectors, light strikes the target object other than where the imaging optics of the CCD-based camera are viewing. Since only a small fraction of the lamps output power is used to illuminate the CCD camera""s field of view, the total output power of the lamps must be very high to obtain the illumination levels required along the field of view of the CCD camera. The balance of the output illumination power is simply wasted in the form of heat.
Most prior art CCD-based hand-held image scanners use an array of light emitting diodes (LEDs) to flood the field of view of the imaging optics in such scanning systems. A large percentage of the output illumination from these LED sources is dispersed to regions other than the field of view of the scanning system. Consequently, only a small percentage of the illumination is actually collected by the imaging optics of the system, Examples of prior art CCD hand-held image scanners employing LED illumination arrangements are disclosed in U.S. Pat. Nos. Re. 36,528, 5,777,314, 5,756,981, 5,627,358, 5,484,994, 5,786,582, and 6,123,261 to Roustaei, each assigned to Symbol Technologies, Inc. and incorporated herein by reference in its entirety. In such prior art CCD-based hand-held image scanners, an array of LEDs are mounted in a scanning head in front of a CCD-based image sensor that is provided with a cylindrical lens assembly. The LEDs are arranged at an angular orientation relative to a central axis passing through the scanning head so that a fan of light is emitted through the light transmission aperture thereof that expands with increasing distance away from the LEDs. The intended purpose of this LED illumination arrangement is to increase the xe2x80x9cangular distancexe2x80x9d and xe2x80x9cdepth of fieldxe2x80x9d of CCD-based bar code symbol readers. However, even with such improvements in LED illumination techniques, the working distance of such hand-held CCD scanners can only be extended by using more LEDs within the scanning head of such scanners to produce greater illumination output therefrom, thereby increasing the cost, size and weight of such scanning devices.
Similarly; prior art xe2x80x9chold-underxe2x80x9d and xe2x80x9chands-free presentationxe2x80x9d type CCD-based image scanners suffer from shortcomings and drawbacks similar to those associated with prior art CCD-based hand-held image scanners.
Recently, there have been some technological advances made involving the use of laser illumination techniques in CCD-based image capture systems to avoid the shortcomings and drawbacks associated with using sodium-vapor illumination equipment, discussed above. In particular, U.S. Pat. No. 5,988,506 (assigned to Galore Scantec Ltd.), incorporated herein by reference, discloses the use of a cylindrical lens to generate from a single visible laser diode (VLD) a narrow focused line of laser light which fans out an angle sufficient to fully illuminate a code pattern at a working distance. As disclosed, mirrors can be used to fold the laser illumination beam towards the code pattern to be illuminated in the working range of the system. Also, a horizontal linear lens array consisting of lenses is mounted before a linear CCD image array, to receive diffused reflected laser light from the code symbol surface. Each single lens in the linear lens array forms its own image of the code line illuminated by the laser illumination beam. Also, subaperture diaphragms are required in the CCD array plane to (i) differentiate image fields, (ii) prevent diffused reflected laser light from passing through a lens and striking the image fields of neighboring lenses, and (iii) generate partially-overlapping fields of view from each of the neighboring elements in the lens array. However, while avoiding the use of external sodium vapor illumination equipment, prior art laser-illuminated CCD-based image capture system suffers from several significant shortcomings and drawbacks. In particular, it requires very complex image forming optics which makes this system design difficult and expensive to manufacture, and imposes a number of undesirable constraints which are very difficult to satisfy when constructing an auto-focus/auto-zoom image acquisition and analysis system for use in demanding applications.
Thus, there is a great need in the art for an improved method of and system for illuminating the surface of objects during image formation and detection operations, and also an improved method of and system for producing digital images using such improved methods object illumination, while avoiding the shortcomings and drawbacks of prior art illumination, imaging and scanning systems and methodologies.
Accordingly, a primary object of the present invention is to provide an improved method of and system for illuminating the surface of objects during image formation and detection operations and also improved methods of and systems for producing digital images using such improved methods object illumination, while avoiding the shortcomings and drawbacks of prior art systems and methodologies.
Another object of the present invention is to provide such an improved method of and system for illuminating the surface of objects using a linear array of laser light emitting devices configured together to produce a substantially planar beam of laser illumination which extends in substantially the same plane as the field of view of the linear array of electronic image detection cells of the system, along at least a portion of its optical path within its working distance,
Another object of the present invention is to provide such an image producing system, wherein the linear array of electronic image detection cells are realized using charge-coupled device (CCD) technology.
Another object of the present invention is to provide such an improved method of and system for producing digital images of objects using a visible laser diode array for producing a planar laser illumination beam for illuminating the surfaces of such objects, and also an electronic image detection array for detecting laser light reflected off the illuminated objects during illumination and imaging operations.
Another object of the present invention is to provide such an improved method of and system for illuminating the surfaces of object to be imaged, using an array of planar laser illumination arrays which employ VLDs that are smaller, and cheaper, run cooler, draw less power, have longer lifetimes, and require simpler optics (because their frequency bandwidths are very small compared to the entire spectrum of visible light).
Another object of the present invention is to provide such an improved method of and system for illuminating the surfaces of objects to be imaged, wherein the VLD concentrates all of its output power into a thin laser beam illumination plane which spatially coincides exactly with the field of view of the imaging optics of the system, so very little light energy is wasted.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein the working distance of the system can be easily extended by simply changing the beam focusing and imaging optics, and without increasing the output power of the visible laser diode (VLD) sources employed therein.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein each planar laser illumination beam is focused so that the minimum width thereof (e.g. 0.6 mm along its non-spreading direction) occurs at a point or plane which is the farthest object distance at which the system is designed to capture images.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein a fixed focal length imaging subsystem is employed, and the laser beam focusing technique of the present invention helps compensate for decreases in the power density of the incident planar illumination beam due to the fact that the width of the planar laser illumination beam for increasing distances away from the imaging subsystem.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein a variable focal length (i.e. zoom) imaging subsystem is employed, and the laser beam focusing technique of the present invention helps compensate for (i) decreases in the power density of the incident illumination beam due to the fact that the width of the planar laser illumination beam (i.e. beamwidth) along the direction of the beam""s planar extent increases for increasing distances away from the imaging subsystem, and (ii) any 1/r2 type losses that would typically occur when using the planar laser illumination beam of the present invention.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein scanned objects need only be illuminated along a single plane which is coplanar with a planar section of the field of view of the image formation and detection module being used in the PLIIM system.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein low-power, light-weight, high-response, ultra-compact, high-efficiency solid-state illumination producing devices, such as visible laser diodes (VLDs), are used to selectively illuminate ultra-narrow sections of a target object during image formation and detection operations, in contrast with high-power, low-response, heavy-weight, bulky, low-efficiency lighting equipment (e.g. sodium vapor lights) required by prior art illumination and image detection systems.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein the planar laser illumination technique of the present invention enables high-speed modulation of the planar laser illumination beam, and use of simple (i.e. substantially monochromatic) lens designs for substantially monochromatic optical illumination and image formation and detection operations.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein special measures are undertaken to ensure that (i) a minimum safe distance is maintained between the VLDs in each PLIM and the user""s eyes using a light shield, and (ii) the planar laser illumination beam is prevented from directly scattering into the FOV of the image formation and detection module within the system housing.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein the planar laser illumination beam and the field of view of the image formation and detection module do not overlap on any optical surface within the PLIIM system.
Another object of the present invention is to provide a planar laser illumination and imaging (PLIIM) system, wherein the planar laser illumination beams are permitted to spatially overlap with the FOV of the imaging lens of the PLIIM only outside of the system housing, remeasured at a particular point beyond the light transmission window, through which the FOV is projected.
Another object of the present invention is to provide a planar laser illumination (PLIM) system for use in illuminating objects being imaged.
Another object of the present invention is to provide planar laser illumination and substantially-monochromatic imaging system, wherein the monochromatic imaging module is realized as an array of electronic image detection cells (e.g. CCD).
Another object of the present invention is to provide a planar laser illumination and substantially-monochromatic imaging system, wherein the planar laser illumination arrays (PLIAs) and the image formation and detection (IFD) module are mounted in strict optical alignment on an optical bench such that there is substantially no relative motion, caused by vibration or temperature changes, is permitted between the imaging lens within the IFD module and the VLD/cylindrical lens assemblies within the PLIAs.
Another object of the present invention is to provide a planar laser illumination and substantially-monochromatic imaging system, wherein the imaging module is realized as a photographic image recording module.
Another object of the present invention is to provide a planar laser illumination and substantially-monochromatic imaging system, wherein the imaging module is realized as an array of electronic image detection cells (e.g. CCD) having short integration time settings for high-speed image capture operations.
Another object of the present invention is to provide a planar laser illumination and substantially-monochromatic imaging system, wherein a pair of planar laser illumination arrays are mounted about an image formation and detection module having a field of view, so as to produce a substantially planar laser illumination beam which is coplanar with the field of view during object illumination and imaging operations.
Another object of the present invention is to provide a planar laser illumination and monochromatic imaging system, wherein an image formation and detection module projects a field of view through a first light transmission aperture formed in the system housing, and a pair of planar laser illumination arrays project a pair of planar laser illumination beams through second set of light transmission apertures which are optically isolated from the first light transmission aperture to prevent laser beam scattering within the housing of the system.
Another object of the present invention is to provide a planar laser illumination and substantially-monochromatic imaging system, the principle of Gaussian summation of light intensity distributions is employed to produce a planar laser illumination beam having a power density across the width the beam which is substantially the same for both far and near fields of the system.
Another object of the present invention is to provide method of and system for illuminating the surfaces of objects during image formation and detection operations.
Another object of the present invention is to provide method of and system for producing digital images of objects using planar laser illumination beams and electronic image detection arrays.
Another object of the present invention is to provide method of and system for producing a planar laser illumination beam to illuminate the surface of objects and electronically detecting light reflected off the illuminated objects during planar laser beam illumination operations.
Another object of the present invention is to provide hand-held laser illuminated image detection and processing device for use in reading bar code symbols and other character strings.
Another object of the present invention is to provide method of and system for producing images of objects by focusing a planar laser illumination beam within the field of view of an imaging lens so that the minimum width thereof along its non-spreading direction occurs at the farthest object distance of the imaging lens.
Another object of the present invention is to provide planar laser illumination modules for use in electronic imaging systems, and methods of designing and manufacturing the same.
Another object of the present invention is to provide planar laser illumination arrays for use in electronic imaging systems, and methods of designing and manufacturing the same.
Another object of the present invention is to provide a unitary object attribute (i.e. feature) acquisition and analysis system completely contained within in a single housing of compact lightweight construction (e.g. less than 40 pounds).
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, which is capable of (1) acquiring and analyzing in real-time the physical attributes of objects such as, for example, (i) the surface reflectively characteristics of objects, (ii) geometrical characteristics of objects, including shape measurement, (iii) the motion (i.e. trajectory) and velocity of objects, as well as (iv) bar code symbol, textual, and other information-bearing structures disposed thereon, and (2) generating information structures representative thereof for use in diverse applications including, for example, object identification, tracking, and/or transportation/routing operations.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, wherein a multi-wavelength i.e. color-sensitive) Laser Doppler Imaging and Profiling (LDIP) subsystem is provided for acquiring and analyzing (in real-time) the physical attributes of objects such as, for example, (i) the surface reflectively characteristics of objects, (ii) geometrical characteristics of objects, including shape measurement, and (iii) the motion (i.e. trajectory) and velocity of objects.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, wherein an image formation and detection (i.e. camera) subsystem is provided having (i) a planar laser illumination and monochromatic imaging (PLIIM) subsystem, (ii) intelligent auto-focus/auto-zoom imaging optics, and (iii) a high-speed electronic image detection array with height/velocity-driven photo-integration time control to ensure the capture of images having constant image resolution (i.e. constant dpi) independent of package height.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, wherein an advanced image-based bar code symbol decoder is provided for reading 1-D and 2-D bar code symbol labels on objects, and an advanced optical character recognition (OCR) processor is provided for reading textual information, such as alphanumeric character strings, representative within digital images that have been captured and lifted from the system.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system for use in the high-speed parcel, postal and material handling industries.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, which is capable of being used to identify, track and route packages, as well as identify individuals for security and personnel control applications.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system which enables bar code symbol reading of linear and two-dimensional bar codes, OCR-compatible image lifting, dimensioning, singulation, object (e.g. package) position and velocity measurement, and label-to-parcel tracking from a single overhead-mounted housing measuring less than or equal to 20xe2x80x3 in width, 20xe2x80x3 in length, and 8xe2x80x3 in height.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system which employs a built-in source for producing a planar laser illumination beam that is coplanar with the field of view of the imaging optics used to form images on an electronic image detection array, thereby eliminating the need for large, complex, high-power power consuming sodium vapor lighting equipment used in conjunction with most industrial CCD cameras.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, wherein the all-in-one (i.e. unitary) construction simplifies installation, connectivity, and reliability for customers as it utilizes a single input cable for supplying input (AC) power and a single output cable for outputting digital data to host systems.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, wherein such systems can be configured to construct multi-sided tunnel-type imaging systems, used in airline baggage handling systems, as well as in postal and parcel identification, dimensioning and sortation systems.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system, for use in (i) automatic checkout solutions installed within retail shopping environments (e.g. supermarkets), (ii) security and people analysis applications, (iii) object and/or material identification and inspection systems, as well as (iv) diverse portable, in-counter and fixed applications in virtual any industry.
Another object of the present invention is to provide such a unitary object attribute acquisition and analysis system in the form of a high-speed package dimensioning and identification system, wherein the PLIIM subsystem projects a field of view through a first light transmission aperture formed in the system housing, and a pair of planar laser illumination beams through second and third light transmission apertures which are optically isolated from the first light transmission aperture to prevent laser beam scattering within the housing of the system, and the LDIP subsystem projects a pair of laser beams at different angles through a fourth light transmission aperture.
Another object of the present invention is to provide a fully automated unitary-type package identification and measuring system (i.e. contained within a single housing or enclosure), wherein a PLIIM-based scanning subsystem is used to read bar codes on packages passing below or near the system, while a package dimensioning subsystem is used to capture information about attributes (i.e. features) about the package prior to being identified.
Another object of the present invention is to provide such an automated package identification and measuring system, wherein Laser Detecting And Ranging (LADAR-based) scanning methods are used to capture two-dimensional range data maps of the space above a conveyor belt structure, and two-dimensional image contour tracing methods are used to extract package dimension data therefrom.
Another object of the present invention is to provide such a unitary system, wherein the package velocity is automatically computed using a pair of laser beams projected at different angular projections over the conveyor belt.
Another object of the present invention is to provide such system in which lasers beams having multiple wavelengths are used to sense packages having a wide range of reflectivity characteristics.
Another object of the present invention is to provide improved image-based hand-held scanners, body-wearable scanners, presentation-type scanners, and hold-under scanners which embody the PLIIM subsystem of the present invention.
Another object of the present invention is to provide a novel planar laser illumination and imaging system (PLIIM) which employs a planar laser illumination array (PLIA) that effectively reduces the speckle-noise pattern observed at the image detection array of the PLIIM system by destroying the spatial and/or temporal coherence of the laser illumination sources in the PLIA that are used to generate planar laser illumination beams (PLIBs) within the PLIIM system.
Another object of the present invention is to provide such PLIIM-based system, wherein the spatial coherence of the laser illumination sources is destroyed by creating multiple xe2x80x9cvirtualxe2x80x9d illumination sources that illuminate the object at different points in space, over the photo-integration time period of the electronic image detection array used in the system.
Another object of the present invention is to provide such a PLIIM-based system, wherein the individual beam components within the composite planar laser illumination beam produced by the PLIA are (i) micro-oscillated (i.e. moved) along the planar extent thereof by an amount of distance xcex94x which is sufficient to cause a difference in phase among the wavefronts of the individual beam component by an amount on the order of xc2xd of the laser illumination wavelength, and (ii) at a rate of change which is greater than or equal to the inverse of the photo-integration time period of the detector elements.
Another object of the present invention is to provide such a PLIIM-based system, wherein under such conditions, the target object is repeatedly illuminated with laser light apparently originating from different points in space over the photo-integration time period of each detector element in the linear image detection array of the PLIIM system, during which reflected laser illumination is received at the detector element. As the relative phase delays between these virtual illumination sources are changing over the photo-integration time period of each image detection element, these virtual sources are effectively rendered spatially incoherent with each other. On a time-average basis, the coherent addition of laser illumination from such moving virtual illumination sources, causes a change in the illumination field detected at each image detection element in the IFD module (i.e. digital camera subsystem). This destroys the spatial coherence of the laser illumination beam received at the detector elements and thereby reduces the speckle-noise pattern (i.e. level) produced thereat. As speckle noise patterns are roughly uncorrelated at the image detector, the reduction in speckle noise amplitude should be proportional to the square root of the number of independent virtual laser illumination sources contributing to the illumination of the target object and formation of the image frame thereof.
Another object of the present invention is to provide such a PLIIM-based system, wherein the xe2x80x9ctemporalxe2x80x9d coherence of the illumination sources is destroyed by creating multiple xe2x80x9cvirtualxe2x80x9d illumination sources that illuminate the object at different moments in time, over the photo-integration time period of the electronic image detection array used in the system.
Another object of the present invention is to provide such a PLIIM-based system, wherein (i) the wavefront of each individual beam component within the composite planar laser illumination beam produced by the PLIA is either amplitude modulated (AM) at a depth of modulation xcex94m (for case of AM), frequency modulated (FM) by an amount of frequency shift xcex94f (for the case of FM) or phase modulated (PM) by an amount of phase shift xcex94xcfx86 (for the case of PM) which is sufficient to cause a different in phase among the wavefronts of the individual beam component by an amount on the order of xc2xd of the laser illumination wavelength, and (ii) wherein the rate of change in such wavefront modulation is greater than or equal to the inverse of the photo-integration time period of the detector elements.
Another object of the present invention is to provide such a PLIIM-based system, wherein under such conditions, the target object is repeatedly illuminated with laser light apparently originating from different moments in time over the photo-integration time period of each detector element in the linear image detection array of the PLIIM system, during which reflected laser illumination is received at the detector element. As the relative phase delays between these virtual illumination sources are changing over the photo-integration time period of each image detection element, these virtual sources are effectively rendered spatially incoherent with each other. On a time-average basis, the coherent addition of laser illumination from such moving virtual illumination sources, causes a change in the illumination field detected at each image detection element in the IFD module (i.e. digital camera subsystem). This destroys the spatial coherence of the laser illumination beam received at the detector elements and thereby reduces the speckle-noise pattern (i.e. level) produced thereat. As speckle noise patterns are roughly uncorrelated at the image detector, the reduction in speckle noise amplitude should be proportional to the square root of the number of independent virtual laser illumination sources contributing to the illumination of the target object and formation of the image frame thereof.
Another object of the present invention is to provide a unitary (PLIIM-based) package dimensioning and identification system, wherein the various information signals are generated by the LDIP subsystem, and provided to the Camera Control (Computer) Subsystem, and wherein the Camera Control Computer generates digital camera control signals which are provided to the image formation and detection (IFD subsystem (i.e. xe2x80x9ccameraxe2x80x9d) so that the system can carry out its diverse functions in an integrated manner, including (1) capturing digital images having (i) square pixels (i.e. 1:1 aspect ratio) independent of package height or velocity, (ii) significantly reduced speckle-noise levels, and (iii) constant image resolution measured in dots per inch (DPI) independent of package height or velocity and without the use of costly telecentric optics employed by prior art systems, (2) automatic cropping of captured images so that only regions of interest reflecting the package or package label are transmitted to either a image-processing based 1-D or 2-D bar code symbol decoder or an optical character recognition (OCR) image processor, and (3) automatic image lifting operations.
As will be described in greater detail in the Detailed Description of the Illustrative Embodiments set forth below, such objectives are achieved in novel methods of and systems for illuminating objects (e.g. bar coded packages, textual materials, graphical indicia, etc.) using planar laser illumination beams (PLIBs) having substantially-planar spatial distribution characteristics that extend through the field of view (FOV) of image formation and detection modules (e.g. realized within a CCD-type digital electronic camera, or a 35 mm optical-film photographic camera) employed in such systems.
In each illustrative embodiment of the present invention, the substantially planar laser illumination beams are preferably produced from a planar laser illumination beam array (PLIA) comprising a plurality of planar laser illumination modules (PLIMs). Each PLIM comprises a visible laser diode (VLD), a focusing lens, and a cylindrical optical element arranged therewith. The individual planar laser illumination beam components produced from each PLIM are optically combined within the PLIA to produce a composite substantially planar laser illumination beam having substantially uniform power density characteristics over the entire spatial extend thereof and thus the working range of the system.
Preferably, each planar laser illumination beam component is focused so that the minimum beam width thereof occurs at a point or plane which is the farthest or maximum object distance at which the system is designed to acquire images. In the case of both fixed and variable focal length imaging systems, this inventive principle helps. compensate for decreases in the power density of the incident planar laser illumination beam due to the fact that the width of the planar laser illumination beam increases in length for increasing object distances away from the imaging subsystem.
By virtue of the novel principles of the present invention, it is now possible to use both VLDs and high-speed CCD-type image detectors in conveyor, hand-held and hold-under type scanning applications alike, enjoying the advantages and benefits that each such technology has to offer, while avoiding the shortcomings and drawbacks hitherto associated therewith.
These and other objects of the present invention will become apparent hereinafter and in the Claims to Invention.